1. Field of the Invention
The present invention relates to a webbing take-up device that takes up and stores webbing.
2. Related Art
A webbing take-up device configuring a vehicle seatbelt device is equipped with a locking mechanism such as an emergency locking retractor (this type of locking mechanism is referred to below as an “ELR mechanism”) that is actuated to restrict rotation of a spool in a pull-out direction when the vehicle decelerates suddenly, or when the spool that takes up and stores the webbing is rotated sharply in the pull-out direction. There is also a locking mechanism such as an automatic locking retractor (this type of locking mechanism is referred to below as an “ALR mechanism”) that, unlike the ELR mechanism, in an actuated state always permits rotation of the spool only in a take-up direction, whilst restricting rotation of the spool in the pull-out direction. Recently, ALR mechanisms are being employed for example for fixing a child seat mounted on a vehicle seat.
In the ELR mechanism and the ALR mechanism, structural components are common with configuration wherein the locking mechanism is forcibly actuated in a state in which a specific length of webbing has been pulled out (for example a state in which the entire webbing has been pulled out from the spool), and the actuated state of the locking mechanism is maintained up to the point at which a specific length of the webbing has been taken up onto the spool.
Configurations employing a planetary gear mechanism are used for switching between the ELR mechanism and the ALR mechanism (see for example Japanese Patent Application Laid-Open (JP-A) No. 7-277137). In such configurations, a sun gear that rotates integrally with the spool configures an input gear of the planetary gear mechanism, and a carrier plate that supports a planet gear configures the output of the planetary gear mechanism. Rotation of the spool in the pull-out direction is transmitted to the carrier plate with being reduced, and when a specific length of the webbing has been pulled out, the carrier plate operates a switching section that switches between the ELR mechanism and the ALR mechanism, thereby switching from the ELR mechanism to the ALR mechanism. The carrier plate operates the switching section and switches from the ALR mechanism to the ELR mechanism when the spool has rotated in the take-up direction to the point at which a specific amount of webbing has been taken up onto the spool from the ALR mechanism state.
Generally, planetary gear mechanisms are configured such that a planet gear meshes with a sun gear, and the planet gear also meshes with an internal-toothed gear that is coaxial to the sun gear. The planetary gear mechanism can thus be achieved (can operate) with a single planet gear. However, in a case in which there is a single planet gear present, displacement of the internal-toothed gear may occur such that, at the meshing portion of the planet gear and the internal-toothed gear, the internal-toothed gear moves apart therefrom in the internal-toothed gear radial direction. In consideration of this issue, the rigidity of each gear, and the rigidity of portions that support each of the gears configuring the planetary gear mechanism is set high in such configurations. It is accordingly difficult to achieve a small size for each of the gears.
Configuration may be made wherein for example two planet gears are disposed facing each other across the sun gear. In such a configuration, when displacement of the internal-toothed gear occurs such that, at the meshing portion of the internal-toothed gear and one of the planet gears, the internal-toothed gear moves apart therefrom in the internal-toothed gear radial direction, the internal-toothed gear presses the other planet gear towards the sun gear side. The thus pressed other planet gear presses the sun gear towards the one planet gear side, and the sun gear then presses the one planet gear towards the internal-toothed gear meshing portion side. Accordingly, in such a configuration, the pressing force of the sun gear acts to maintain the meshing of the one planet gear and the internal-toothed gear even when displacement of the internal-toothed gear such as described above occurs.
However, it is difficult to mesh the planet gears properly with both the sun gear and the internal-toothed gear without both appropriate rotation positions of the planet gears about their respective axial centers and appropriate rotation positions of the planet gears about the sun gear. In particular, in a case in which plural planet gears are employed, assembly is difficult from the second planet gear (and the subsequent planet gears).